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8.1 The Nature of the Earth
.A system which is consisted of large number of solar systems is known as a galaxy.
Our solar system belongs to a galaxy called Milky Way.
It has been estimated that the Milky Way galaxy contains about hundred billion stars similar to
our sun.
Contents
The Nature of the Earth
The structure of the Earth
Tectonic plate and plate tectonics
Milky Way galaxy
Taxila Central College – Horana
Grade 7
Unit 08 - The nature of the Earth
Tutorial 08
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Our solar system
The system which is consisted of our sun and eight planets is called our solar system.
All the planets revolve around the sun in their own paths (orbits).
These planets are held in place by the gravitational force of the sun.
Earth
It is the only known planet in the space that contains liquid water. So there is a life on
earth.
There are water falls, mountains, rocks, rivers, lakes and oceans on earth.
The atmosphere of the earth is consisted of a mixture of gases which are important for
the existence of life.(Oxygen, Carbon dioxide, Ozone layer)
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Questions
a) What are the planets found either side of the earth?
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b) Write down the order of the position of eight planets in terms of distance from sun.
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c) What is the place of the earth from the sun in our solar system? …………………………………………….
d) The earth is the most suitable planet for the living beings. What are the flavourable conditions
which are important for the existence of life on earth?
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e) Pluto is not considered as a planet. State the reason.
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8.2 The structure of the earth
How do geologists obtain information about the nature of the inner part of the
earth?
During the earthquakes huge rock movements within the earth give rise to a kind of wave
known as seismic waves.
They travel at different speeds when they pass through different types of materials.
So these waves reach the surface of the earth by passing through various layers in the earth
with different speeds.
Seismometer is used to detect the seismic waves and record the data about the waves in
seismograms.
The scientists study seismograms and learn a lot about earth’s internal structure.
So the geologists obtain information about the nature of the inner part of the earth
by;
Examining different types of rocks which are brought to the
earth surface in times of volcanic eruptions.
By examining earthquakes.
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Internal structure of the Earth
According to the data, the inner part of the earth can be divided into three main layers as
shown below.
Questions
i. What are the three main layers in the inner part of the earth?
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ii. What is the highest place on earth? ....................................................
iii. What is the lowest place on earth? ...................................................
iv. What is the term given to the waves that propagate inner parts of the earth during
earthquakes? ……………………………………………………..
v. What is the instrument that can be used to identify the special wave that you mentioned above?
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vi. Where is the instrument that you mentioned above, installed in Sri Lanka? ………………………………
vii. What objects can be used as a model (replica) to represent the inner parts of the earth?
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viii. What are the resources that we obtain from the earth crust?
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ix. How do geologists obtain information about the nature of the inner part of the earth?
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x. The figure given below shows information on internal structure of the earth. Fill in the blanks.
Thickness of the crust at the
bottom of the ocean is about
……………. and the thickness on
the land is about ……………………
Elements that are present
Crust
…1.Oxygen……
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Mantle
1. Oxygen
…………………………
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.
Core
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2. Nickel
Composition
Crust
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Mantle
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2.Molten rocks
Core
1.…Molten…iron…
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Tectonic plate and plate tectonics
Tectonic plates
There are two types of tectonic plates.
1. Major tectonic plates.
2. Minor tectonic plates.
Plate Tectonic
Major tectonic plates
Assessment
1. Design a three dimensional replica (model) of
the internal structure of the earth.
(Activity 8.2 in science text book)
Tectonic plates are pieces of Earth’s crust and upper mantle, together referred to as the
lithosphere.
Plate Tectonic is a scientific theory describing the large scale motion of seven large plates
and the movement of a larger number of smaller plates of the Earth’s lithosphere.
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1. How many major tectonic plates are there on the earth? .............................................
2. Mention the major tectonic plates of the earth that you mentioned above.
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3. On which tectonic plate that our country is situated? .............................................
4. Why do severe earth quakes not occur in Sri Lanka?
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5. What are the tectonic plates near Sri Lanka, India and Nepal?
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6. In which countries severe earth quakes occur frequently?
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7. The figures given below show the ways of movement of tectonic plates. Identify them.
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Plate Movements
The most of the plate boundaries or margins are at the bottom of the sea.
Tectonic plate margins consist of volcanoes and constant earthquakes occur near them.
The margin of a plate can be seen on the land in North America known as San Andreas
Fault and earth quakes occur frequently near this region.
A B C
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Pacific Plate North American plate
San Andreas Fault
